The present invention relates to an intake air control system to vary the amount of air entering the cylinders of a fuel-injection multi-cylinder internal combustion engine equipped with a cylinder selector when the engine is switched from full-cylinder mode to part-cylinder mode or vice versa in order to maintain the previous level of power output of the engine after the switching.
The power output of the conventional spark-ignited fuel-injection multi-cylinder internal combustion engine is controlled by a throttle valve. At low power output under light load, the throttle valve is nearly closed to restrict the amount of air entering the cylinders. This gives rise to "throttling loss" caused by the engine's expenditure of energy in drawing its air into its cylinders against a high vacuum in the intake manifold (caused by pressure drop across the throttle valve). Because of this, an engine runs most efficiently when unthrottled, i.e., under heavy load. Thus, operating an engine at the unthrottled state will be one of effective ways to cut fuel consumption.
The conventional automotive engine is designed so that it can afford to produce adequate power for the car's demands estimated assuming a wide range of running conditions, and it is not rare to operate an engine at between 1/3 and 1/4 of its rated maximum power output when the car travels at its cruising speed.
It has been proposed that fuel consumption within a light load operating range, can be cut by operating only the reduced number of cylinders at high-per-cylinder output by increasing load-per-cylinder to produce adequate power for the car's demands, by cutting off fuel supply to the remaining cylinders.
The known spark-ignited, fuel-injection automotive internal combustion engines equipped with a cylinder selector system, in which fuel supply to predetermined cylinders is cut off and only air supply to these cylinder continues, have a shortcoming that a reduction in the power by the engine and discontinuity have been experienced upon switching from full-cylinder mode to part-cylinder mode if an operator maintains the same depression degree of an accelerator pedal. Thus, it was necessary to manipulate an accelerator pedal to supply additional amount of air to the cylinders by increasing the opening degree of a throttle valve to increase power-per-cylinder output of the selected cylinders to which fuel injection continues to produce adequate power for the car's demands.